BLEACH DI INFECTION: Despite the fact that bleach is aqueous sodium hypochlorite, the actual disinfecting species in bleach is hypochlorous acid (HOCL) not sodium hypochlorite (Figure 1). When one refers to the free available chlorine in a disinfectant, this denotes the sum of all chlorine species in solution and does not directly relate to the efficacy of a chlorine disinfectant (due to the pH differences that exist in varying solutions). The basic problem plaguing bleach as a disinfectant is due to the fact that the % of hypochlorous acid in solution is severely affected by the pH of the solution. Typical bleach has a very high pH of 9-11 (far too high for any significant HOCL (hypochlorous acid) to be present in solution. In fact, the quantity of HOCL is only 20% at a pH of 8 and degrades to less than 1% at a pH of 11. Consequently, a massive quantity of bleach must be used to deliver a sufficient quantity of active disinfecting chlorine species during a disinfection. In fact, my investigations
Cl2 and H2O
HOCL + HCL
H + + - OCL
reveal that bleach purchased at retail consumer stores is usually degraded and yields only 3-4% hypochlorite in solution and the pH is usually in excess of 11, consequently chemical dilution of the product, itself, has already occured. This is the reason for the caveat that bleach solutions should always be made fresh and tested for available chlorine as an indication of disinfecting capability. Only when the pH drops to around 6.5 does the quantity of hypochlorous acid in solution become substantial and disinfecting power increases drastically. This is the explanation for the successful use of bleach type sanitizers in the swimming pool industry. wimming pool water is acid/base buffered to approximately pH 7 and this allows a good quantity of HOCL to be present for disinfection. This is also the reason for the popularity of chlorine releasing powders such as NaDCC (sodium dichloroisocyanurate) in the field of medical disinfection. These powders are capable of releasing a large quantity of active chlorine disinfecting species in a short time frame without the pH limitations of bleach and its dilutions. Also, point-of-use chlorine generators (essentially buffered and metered release of calcium hypochlorite in aqueous delivery systems) are very effective and are popular in Europe and Africa for cleaning and disinfection of animal barns and outdoor toilet facilities. Chlorine can be a very effective disinfectant, but is clearly dependent on the pH and source of chlorine generation. Bleach solutions deliver the absolute minimum when compared to the chlorine alternatives and is a poor choice (considering the excellent alternatives available) for embalming rooms.
Bleach in Embalming Rooms: Overrated and Overused. Champion Expanding Encyclopedia of Mortuary Practices Number 640, 2000
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